1. Field of the Invention
The present invention relates generally to an actively controlled suspension system which is variable of suspension characteristics depending upon a vehicle driving condition for suppressing vehicular attitude change. More specifically, the invention relates to an actively controlled suspension system which is variable of control characteristics, such as sensitivity of vehicular attitude change, depending upon the vehicle driving condition. Further particularly, the invention relates to a suspension control system performing suspension control including bouncing suppressive control.
2. Description of the Background Art
Actively controlled suspension systems gains popularity in automotive vehicles because of remarkable performance in achieving both of driving stability and riding comfort. Such suspension systems performs various control, such as anti-rolling and/or anti-pitching control, bounding suppressive control and so forth, for regulating vehicular body attitude at various vehicle driving mode condition.
In general, bouncing suppressive suspension control is performed for suppressing relative displacement between a vehicle body and a suspension member which rotatably supports a road wheel. Relative displacement between the vehicle body and a suspension member is monitored by means of a sensor, such as a vertical acceleration sensor, a stroke sensor and so forth. In case that the vertical acceleration sensor is used for monitoring the vertical and relative displacement between the vehicle body and the suspension member, the vertical acceleration value is integrated to obtain data representative of the relative displacement between the vehicle body and the suspension member. Since the suspension control for adjusting stiffness or suspension characteristics depending upon the magnitude of vertical displacement between the vehicle body and the suspension member derived on the basis of the vertical acceleration monitored by the vertical acceleration sensor, failure of the vertical acceleration sensor directly results in malfunctioning of the suspension control. For instance, when the vertical acceleration indicative sensor signal increases in stepwise fashion due to failure of the vertical acceleration sensor, the erroneously increased level of vertical acceleration sensor signal is amplified through the bouncing control system to cause abrupt change of the vehicular height. Such abrupt change in the vehicular height clearly degrades riding comfort and drive feeling. Therefore, in case of failure of the sensor means which causes error in the monitored vehicular driving condition data, fail-safe operation has to be performed for controlling suspension system to predetermined suspension mode for assure safety.